Question

U= {1,2,3,4,5,6,7,8,}, A={1,4,5,7}, B= {2,5,6,7,}, and C= {3,4,6,7}

Complete the following set operations:
a. AU(BUC)
b. (AN(BNC))'
c. (ANB)U(ANC)
d. (ANB')U(ANC')

Answer 1

a. {1, 2, 3, 4, 5, 6, 7}

b. {1, 2, 3, 4, 5, 6, 8}

c. {4, 5, 7}

d. {1, 4, 5}

Explanation:

The union of two sets is the list of elements in either set. The intersection of two sets is the list of elements in both sets. The complement of a set is the list of elements in the universal set that are not in the set being complemented. The complement of a set can be indicated with an apostrophe: A' is the complement of set A, for example.

a. AU(BUC)

B∪C = {2, 5, 6, 7} ∪ {3, 4, 6, 7} = {2, 3, 4, 5, 6, 7}

A∪(B∪C) = {1, 4, 5, 7} ∪ {2, 3, 4, 5, 6, 7} = {1, 2, 3, 4, 5, 6, 7}

b. (AN(BNC))'

B∩C = {2, 5, 6, 7} ∩ {3, 4, 6, 7} = {6, 7}

A ∩ (B∩C) = {1, 4, 5, 7} ∩ {6, 7} = {7}

(A∩(B∩C))' = {7}' = {1, 2, 3, 4, 5, 6, 8}

c. (ANB)U(ANC)

A∩Β = {1, 4, 5, 7} ∩ {2, 5, 6, 7} = {5, 7}

Α∩C = {1, 4, 5, 7} ∩ {3, 4, 6, 7} = {4, 7}

(A∩B)∪(A∩C) = {5, 7} ∪ {4, 7} = {4, 5, 7}

d. (ANB')U(ANC')

(A∩B')∪(A∩C') = A∩(B'∪C') = A∩(B∩C)'

(B∩C)' = {6, 7}' = {1, 2, 3, 4, 5, 8}

A∩(B∩C)' = {1, 4, 5, 7} ∩ {1, 2, 3, 4, 5, 8} = {1, 4, 5}

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Additional comment

In part (d) we made use of De Morgan's law for sets:

B'∪C' = (B∩C)'

We also made use of the distributive property for sets:

A∩(B∪C) = (A∩B)∪(A∩C)